A number of virion phosphotransferase activities as well as protein kinase activities have been reported to be associated with retroviruses. ml-MSV(FeLV) virions produced by the Crandell cat (P521) cell line were purified by isopycnic floatation and after treatment with nucleases and proteases were shown to contain an endogenously active cyclic AMP-independent phosphotransferase activity. Enzymatic properties were investigated and the apparent molecular weight of the activity was 60,000 daltons. Further the enzymatic activity could be immunoprecipitated by an antiserum specific for the mlMSV associated polyprotein, pP60gag. A detergent-solubilized virus as well as an immunoprecipitated complex was capable of endogenously phosphokinasing a P60 and p12 dalton protein. Additionally the enzyme is capable of phosphokinasing exogenous substrates such as lambda casein, phosvitin, histone-proteins and protamine sulfate. No similar activities were found associated with anti-pP60 immunoprecipitates from non-infected or leukemia-infected cells. Using RNA derived from cells infected with the HT-l (P-) and ml strain of Moloney sarcoma virus (ml-MSV) we have been able to stimulate the synthesis of several polypeptides in a messenger--dependent lysate (MDL) reticulocyte cell-free system. Also specific DNA restriction fragments of cloned ml-MSV and HT-l genomes have been isolated and covalently bound to diazobenzyloxymethyl cellulose resin. This resin has been used to isolate specific mRNA species from a total population of polyadenylated mRNA derived from P521 and HTMF cells. Products specified by such mRNA isolates are being characterized in MDL-derived from reticulocyte and wheat germ embryo cell-free extracts.